JP2017116705A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress damage to a contact member compared with a case where a roller in contact with the contact member with a belt therebetween rotates in the reverse direction at switching of an image forming mode.SOLUTION: An image forming apparatus comprises: an intermediate transfer belt 21 that is stretched over a plurality of rollers; driving means that drives to rotate the intermediate transfer belt 21; a belt cleaning device that is in contact with a surface of a belt stretched over one roller of the plurality of rollers; and switching means that displaces at least one roller of the plurality of rollers to switch an image forming mode. At switching performed by the switching means, the driving means rotates the intermediate transfer belt 21 in the normal direction at a speed higher than the rotation speed at which the roller in contact with the belt cleaning device rotates in the reverse direction.SELECTED DRAWING: Figure 23

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, some image forming apparatuses are configured to move some of a plurality of rolls that stretch an intermediate transfer belt when switching from a full color mode to a monochrome mode. As techniques related to such an image forming apparatus, for example, those disclosed in Patent Documents 1 and 2 have already been proposed.

  Japanese Patent Laid-Open No. 2004-260688 realizes a means for separating foreign matter adhering to the tip of the cleaner blade with a simple configuration and simplifies the apparatus configuration and reduces the cost. After the image forming operation is executed, the transfer belt is pushed to and brought into contact with the image forming station by the transfer member to allow the primary transfer of the toner image at all the image forming stations. When necessary, the transfer member is moved away from the image forming station to eliminate the pushing state of the transfer belt by the transfer member, so that the transfer roller is tensioned by the urging force from the urging means. Following movement in the urging direction and driven rotation in the direction opposite to the conveying direction, the blade facing roller is set in a direction opposite to the urging direction. By releasing movement is obtained by adapted to release the tension on the transfer belt applied to the transfer belt from the blade facing roller.

  Japanese Patent Application Laid-Open No. 2004-260688 discloses an image carrier that carries a toner image on the surface thereof, a first drive unit that drives the image carrier, and an image carrier that suppresses a reduction in device life due to rubbing between driving components. First speed detecting means for detecting a physical quantity corresponding to the peripheral speed, a belt disposed opposite to the image carrier, a belt roller for supporting the belt, a second driving means for driving the belt, and the progress of the belt The second speed detection means for detecting a physical quantity corresponding to the speed, and a contact state in which the image carrier and the belt are in contact with each other, or a contact state in which the image carrier and the belt are separated from each other. And a control unit that controls the operation of the entire apparatus. When the image carrier and the belt are switched from the separated state to the contact state, the control unit controls the first driving unit to control the image carrier. The peripheral speed of the first predetermined And the second driving means is controlled to set the belt traveling speed to a predetermined second value, and then the contact / separation mechanism is operated to bring the image carrier and the belt into contact with each other. Is.

JP 2007-93782 A JP 2007-57652 A

  An object of the present invention is to suppress damage to a contact member as compared with a case where a roll with which the contact member contacts via a belt rotates in the reverse direction when the image forming mode is switched.

The invention described in claim 1 is an endless belt stretched around a plurality of rolls;
Drive means for rotationally driving the belt;
A contact member that contacts a surface of a belt stretched around one of the plurality of rolls;
Switching means for switching an image forming mode by displacing at least one of the plurality of rolls;
With
The image forming apparatus in which the belt is rotated in the forward direction by the driving unit at a speed equal to or higher than a rotation speed at which the roll with which the contact member contacts via the belt rotates in the reverse direction when switching by the switching unit.

  According to a second aspect of the present invention, the belt is stretched around a plurality of rolls including a tension applying roll, and the contact member is in contact with the belt stretched around the tension applying roll. The image forming apparatus according to Item 1.

According to a third aspect of the present invention, the image forming apparatus has a full color mode and a monochrome mode as an image forming mode.
The image forming apparatus according to claim 1, wherein the switching unit switches the image forming mode to the monochrome mode at the end of the image forming operation in the full color mode.

  According to the fourth aspect of the present invention, when the image forming mode is switched from the full color mode to the monochrome mode, the roll disposed adjacent to the downstream side in the belt moving direction of the tension applying roll is in the retracted position. The image forming apparatus according to claim 1, wherein the image forming apparatus is moved.

  According to the first aspect of the present invention, it is possible to suppress damage to the contact member as compared with the case where the roll with which the contact member contacts via the belt rotates in the reverse direction when the image forming mode is switched. .

  According to the second aspect of the present invention, the configuration of the roll that stretches the belt can be simplified as compared with the case where the contact member is brought into contact with the drive roll.

  According to the third aspect of the present invention, the switching unit can immediately start the monochrome mode at the end of the image forming operation in the full color mode as compared with the case where the image forming mode is not switched to the monochrome mode. .

  According to the invention described in claim 4, the damage of the contact member caused by the movement of the roll disposed adjacent to the downstream side of the tension applying roll along the belt moving direction to the retracted position is suppressed. Can do.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. 1 is a configuration diagram illustrating an image forming unit of an image forming apparatus according to Embodiment 1 of the present invention; FIG. 2 is a configuration diagram illustrating an image forming unit of the image forming apparatus in a black and white mode. FIG. 3 is a perspective configuration diagram illustrating an intermediate transfer unit. FIG. 3 is a perspective configuration diagram illustrating an intermediate transfer unit with an intermediate transfer belt removed. FIG. 2 is a configuration diagram illustrating an intermediate transfer unit in a full color mode. FIG. 3 is a configuration diagram illustrating an intermediate transfer unit in a monochrome mode. It is a perspective block diagram which shows the drive motor of a drive device. It is a block diagram which shows a drive device. FIG. 3 is a perspective configuration diagram illustrating a driving force transmission mechanism of a photosensitive drum. It is a perspective block diagram which shows the member which comprises a driving force transmission mechanism. FIG. 3 is a perspective configuration diagram illustrating a driving force transmission mechanism of a photosensitive drum. It is a perspective view showing a driving force transmission mechanism of the developing device. It is a block diagram which shows a drive switching apparatus. It is a perspective lineblock diagram showing a tooth missing gear. It is a perspective block diagram which shows a drive device. It is a timing chart which shows operation | movement of a drive switching device. It is a perspective block diagram which shows operation | movement of a drive switching apparatus. It is a perspective block diagram which shows operation | movement of a drive switching apparatus. It is a perspective block diagram which shows operation | movement of a drive switching apparatus. It is a perspective block diagram which shows operation | movement of a drive switching apparatus. It is a perspective block diagram which shows operation | movement of a drive switching device. It is a block diagram which shows the movement of a tension | tensile_strength provision roll. It is a block diagram which shows the cleaning board which contacts a tension | tensile_strength provision roll.

  Embodiments of the present invention will be described below with reference to the drawings.

[Embodiment 1]
1 and 2 show an image forming apparatus according to the first embodiment. FIG. 1 shows an outline of the entire image forming apparatus, and FIG. 2 shows an enlarged main part (image forming apparatus, etc.) in the image forming apparatus.

<Overall Configuration of Image Forming Apparatus>
The image forming apparatus 1 according to the first embodiment is configured as a color printer, for example. The image forming apparatus 1 holds a plurality of image forming apparatuses 10 that form toner images developed with toner constituting the developer 4 and the toner images formed by the respective image forming apparatuses 10 and finally An intermediate transfer device 20 that transports to a recording sheet 5 as an example of a recording medium to a secondary transfer position for secondary transfer, and a required recording sheet 5 that should be supplied to the secondary transfer position of the intermediate transfer device 20 is accommodated and transported. And a fixing device 40 for fixing the toner image on the recording paper 5 secondarily transferred by the intermediate transfer device 20. In the figure, reference numeral 1a denotes an apparatus main body of the image forming apparatus 1. The apparatus main body 1a is formed of a support structure member, an exterior cover, and the like. A broken line in the figure indicates a main conveyance path through which the recording paper 5 is conveyed in the apparatus main body 1a.

  The image forming device 10 includes four image forming devices 10Y, 10M, 10C, and 10K that respectively form four color toner images exclusively for yellow (Y), magenta (M), cyan (C), and black (K). It is configured. These four image forming apparatuses 10 (Y, M, C, K) are arranged so as to be arranged in a line in an inclined state in the internal space of the apparatus main body 1a.

  The four image forming devices 10 are composed of yellow (Y), magenta (M) and cyan (C) color image forming devices 10 (Y, M, C) and a black (K) image forming device 10K. Has been. The black image forming device 10 </ b> K is disposed on the most downstream side in the moving direction B of the intermediate transfer belt 21 of the intermediate transfer device 20. The image forming apparatus 1 operates as a color forming apparatus 10 (Y, M, C) and a black (K) image forming apparatus 10K by operating a color image forming apparatus 10 (Y, M, C) and a black (K) And a monochrome mode in which only the image forming apparatus 10K of K) is operated to form a monochrome image.

  Each image forming apparatus 10 (Y, M, C, K) includes a rotating photosensitive drum 11 as an example of an image holding member as shown in FIGS. 1 and 2, and this photosensitive drum 11. Each apparatus as an example of the following toner image forming means is mainly disposed around the apparatus. The main devices are a charging device 12 that charges a peripheral surface (image holding surface) on the photosensitive drum 11 on which an image can be formed to a required potential, and image information (on the charged peripheral surface of the photosensitive drum 11). Exposure apparatus 13 that irradiates light based on (signal) to form an electrostatic latent image (for each color) having a potential difference, and developer of the corresponding color (Y, M, C, K). A developing device 14 (Y, M, C, K) that is developed with toner 4 to form a toner image, and a primary transfer device 15 (Y) as an example of a primary transfer unit that transfers each toner image to the intermediate transfer device 20. , M, C, K) and a drum cleaning device 16 (Y, M, C, K) that removes and removes adhering matters such as toner remaining on the image holding surface of the photosensitive drum 11 after the primary transfer. Etc.

  The photosensitive drum 11 is formed by forming an image holding surface having a photoconductive layer (photosensitive layer) made of a photosensitive material on the peripheral surface of a cylindrical or columnar base material to be grounded. The photosensitive drum 11 is supported so as to rotate in a direction indicated by an arrow A when power is transmitted from a driving device (not shown).

  The charging device 12 includes a contact-type charging roll that is disposed in contact with the photosensitive drum 11. The charging device 12 has a cleaning roll 121 that cleans its surface. A charging voltage is supplied to the charging device 12. As the charging voltage, when the developing device 14 performs reversal development, a voltage or current having the same polarity as the charging polarity of the toner supplied from the developing device 14 is supplied. As the charging device 12, a non-contact type charging device such as a scorotron disposed in a non-contact state on the surface of the photosensitive drum 11 may be used.

  The exposure device 13 irradiates the photosensitive drum 11 with light corresponding to image information by LEDs (Light Emitting Diodes) as a plurality of light emitting elements arranged along the axial direction of the photosensitive drum 11 to electrostatic latent images. The LED print head is formed. As the exposure device 13, a device that deflects and scans laser light configured according to image information along the axial direction of the photosensitive drum 11 may be used.

  As shown in FIG. 2, each of the developing devices 14 (Y, M, C, K) holds the developer 4 inside a housing 140 in which an opening and a storage chamber for the developer 4 are formed. A developing roll 141 that conveys the developer 4 to a developing area facing the photosensitive drum 11, two agitating and conveying members 142 and 143 such as two screw augers that convey the developer 4 while passing the developing roll 141 while stirring, and a developing roll 141. A layer thickness regulating member 144 that regulates the amount (layer thickness) of the developer held on the substrate is arranged. A developing voltage is supplied to the developing device 14 from a power supply device (not shown) between the developing roll 141 and the photosensitive drum 11. Further, the developing roll 141 and the agitating / conveying members 142 and 143 are rotated in a required direction by receiving power from a driving device (not shown). Further, as the four-color developer 4 (Y, M, C, K), a two-component developer containing a nonmagnetic toner and a magnetic carrier is used.

  The primary transfer device 15 (Y, M, C, K) is in contact with the periphery of the photosensitive drum 11 via an intermediate transfer belt 21 and rotates, and a contact type provided with a primary transfer roll to which a primary transfer voltage is supplied. This is a transfer device. As the primary transfer voltage, a DC voltage having a polarity opposite to the charging polarity of the toner is supplied from a power supply device (not shown).

  As shown in FIG. 2, the drum cleaning device 16 is disposed so as to be in contact with the peripheral surface of the photosensitive drum 11 after the primary transfer with a container-shaped main body 160 that is partially opened at a required pressure. A cleaning plate 161 that removes and removes deposits such as toner, and a sending member 162 such as a screw auger that collects and removes deposits such as toner removed by the cleaning plate 161 and sends them to a collection system (not shown). ing. As the cleaning plate 161, a plate-like member (for example, a blade) made of a material such as rubber is used.

  As shown in FIG. 1, the intermediate transfer device 20 is disposed so as to exist at a position above each image forming device 10 (Y, M, C, K). The intermediate transfer device 20 includes an intermediate transfer belt 21 that rotates in a direction indicated by an arrow B while passing a primary transfer position between the photosensitive drum 11 and the primary transfer device 15 (primary transfer roll), and an intermediate transfer belt 21. Are arranged on the outer peripheral surface (image holding surface) side of the intermediate transfer belt 21 supported by the belt support roll 22 and a plurality of belt support rolls 22 to 25 that hold the belt in a desired state from the inner surface thereof and rotatably support the belt. The secondary transfer device 26 as an example of a secondary transfer means for secondary transfer of the toner image on the intermediate transfer belt 21 to the recording paper 5 and the outer peripheral surface of the intermediate transfer belt 21 after passing through the secondary transfer device 26 And a belt cleaning device 27 that removes and adheres toner, paper dust, and other adhering matter.

  As the intermediate transfer belt 21, for example, an endless belt made of a material in which a resistance adjusting agent such as carbon black is dispersed in a synthetic resin such as polyimide resin or polyamide resin is used. The belt support roll 22 is configured as a drive roll that is rotationally driven by a driving device (not shown) that also serves as a back support roll for secondary transfer, and the belt support roll 23 is configured as a tension applying roll that applies tension to the intermediate transfer belt 21. The belt support rolls 24 and 25 are configured as first and second surface-developing rolls that form the image forming surface of the intermediate transfer belt 21. The belt support roll 23 also serves as an opposing roll that faces the cleaning plate 271 of the belt cleaning device 27.

  As described later, the first surface roll 24 is a primary transfer roll 15 (Y, M, C) of yellow (Y), magenta (M), and cyan (C) colors in the monochrome image forming mode. ) And the intermediate transfer belt 21 can be moved to a retracted position for separating the intermediate transfer belt 21 from the photosensitive drum 11 (Y, M, C).

  As shown in FIG. 1, the secondary transfer device 26 is configured to move the intermediate transfer belt 21 at a secondary transfer position that is an outer peripheral surface portion of the intermediate transfer belt 21 supported by the belt support roll 22 in the intermediate transfer device 20. It is a contact type transfer device provided with a secondary transfer roll that rotates in contact with a peripheral surface and is supplied with a secondary transfer voltage. The secondary transfer roll 26 or the belt support roll 22 of the intermediate transfer device 20 is supplied with a DC voltage having the opposite polarity or the same polarity as the toner charging polarity from a power supply device (not shown) as a secondary transfer voltage. .

  As shown in FIG. 2, the belt cleaning device 27 is disposed so as to be in contact with the container-shaped main body 270 that is partially opened and the peripheral surface of the intermediate transfer belt 21 after the secondary transfer with a required pressure. A cleaning plate 271 as an example of a contact member that removes and removes adhering matter such as residual toner and a screw auger that collects and removes adhering material such as toner removed by the cleaning plate 271 and sends it to a collecting system (not shown). It consists of a delivery member 272 and the like. As the cleaning plate 271, a plate-like member (for example, a blade) made of a material such as rubber is used. The cleaning plate 271 has a base end attached to the main body 270, and a front end portion disposed toward the upstream side along the moving direction of the intermediate transfer belt 21, and an edge positioned at the front end of the cleaning plate 271. The portion constitutes a so-called doctor blade that contacts the intermediate transfer belt 21 from the downstream side to the upstream side in the moving direction of the intermediate transfer belt 21.

  The fixing device 40 is heated by a heating unit so as to rotate in a direction indicated by an arrow and maintain a surface temperature at a predetermined temperature inside a housing (not shown) in which an inlet and an outlet for the recording paper 5 are formed. A roll-form or belt-form heating rotator 41 and a roll-form or belt-form pressurizing rotator 42 that is driven and rotated in contact with a predetermined pressure in a state substantially along the axial direction of the heating rotator 41. Are arranged. In the fixing device 40, the contact portion where the heating rotator 41 and the pressing rotator 42 come into contact becomes a fixing processing unit that performs a required fixing process (heating and pressing).

  The paper feeding device 30 is disposed so as to exist at a position below the image forming device 10 (Y, M, C, K). This paper feeding device 30 is a single (or plural) paper container 31 that accommodates recording papers 5 of a desired size and type, and sends out the recording paper 5 from the paper container 31 one by one. The apparatus 32 is mainly configured. For example, the paper container 31 is attached so that it can be pulled out to the front side (side surface on which the user faces during operation) of the apparatus main body 1a.

  Examples of the recording paper 5 include thin paper such as plain paper and tracing paper used for electrophotographic copying machines and printers, or an OHP sheet. In order to further improve the smoothness of the image surface after fixing, the surface of the recording paper 5 is preferably as smooth as possible. For example, coated paper in which the surface of plain paper is coated with resin, art paper for printing, etc. So-called cardboard having a relatively large basis weight can be suitably used.

  Between the paper feeding device 30 and the secondary transfer device 26, the recording paper 5 fed from the paper feeding device 30 is composed of one or a plurality of paper transporting roll pairs 33 for transporting the recording paper 5 to the secondary transfer position, and a transport guide (not shown). A paper feed conveyance path 34 is provided. The pair of sheet conveyance rolls 33 arranged at the position immediately before the secondary transfer position in the sheet conveyance path 34 is configured as a roll (registration roll) that adjusts the conveyance timing of the recording sheet 5, for example. Further, between the secondary transfer device 26 and the fixing device 40, a paper transport path 35 for transporting the recording paper 5 after the secondary transfer sent from the secondary transfer device 26 to the fixing device 40 is provided. Yes. Further, in a portion near the discharge port of the sheet formed on the image forming apparatus main body 1a, the fixed recording sheet 5 fed from the fixing device 40 by the exit roll 36 is fed to the upper sheet discharge section 37 of the image forming apparatus main body 1a. A discharge conveyance path 39 provided with a pair of paper discharge rolls 38 for discharging the paper is provided.

  A switching gate 43 is provided between the fixing device 40 and the paper discharge roll pair 38 to switch the paper transport path. The pair of paper discharge rolls 38 is configured so that the rotation direction can be switched between a normal rotation direction (discharge direction) and a reverse rotation direction. When images are formed on both sides of the recording paper 5, after the rear end of the recording paper 5 having an image formed on one side passes through the switching gate 43, the rotation direction of the paper discharge roll pair 38 is set to the normal rotation direction (discharge). Direction) to reverse direction. The recording paper 5 transported in the reverse direction by the paper discharge roll pair 38 is transported for both sides formed so that the transport path is switched by the switching gate 43 and along the side surface of the image forming apparatus main body 1a. It is conveyed to the path 44. The double-sided conveyance path 44 includes sheet conveyance roll pairs 45 to 47 that convey the recording sheet 5 to the sheet conveyance roll pair 33 in a state where the front and back sides are reversed, a conveyance guide (not shown), and the like.

  In FIG. 1, reference numerals 145 (Y, M, C, K) are arranged in a plurality along a direction orthogonal to the paper surface and include at least toner supplied to the corresponding developing devices 14 (Y, M, C, K). Each toner cartridge containing a developer is shown.

  Further, reference numeral 200 in FIG. 1 indicates a control device that comprehensively controls the operation of the image forming apparatus 1. The control device 200 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a bus connecting these CPU and ROM, a communication interface, and the like (not shown).

<Operation of Image Forming Apparatus>
Hereinafter, a basic image forming operation by the image forming apparatus 1 will be described.

  Here, first, a full color image formed by combining toner images of four colors (Y, M, C, K) is formed using the four image forming devices 10 (Y, M, C, K). The operation in the full color mode will be described.

[Full color mode]
When the image forming apparatus 1 receives command information for a request for a full-color image forming operation (printing) from a user interface (not shown) or a printer driver, the image forming apparatus 10 (Y, M, C, K), intermediate transfer The device 20, the secondary transfer device 26, the fixing device 40, etc. are started.

  In each image forming device 10 (Y, M, C, K), as shown in FIGS. 1 and 2, first, each photosensitive drum 11 rotates in the direction indicated by arrow A, and each charging device 12. Charges the surface of each photosensitive drum 11 to a required polarity (negative polarity in the first embodiment) and potential. Subsequently, the exposure apparatus 13 converts the image information input to the image forming apparatus 1 into each color component (Y, M, C, K) with respect to the surface of the photosensitive drum 11 after charging. The light emitted on the basis of the signal is irradiated to form an electrostatic latent image of each color component composed of a required potential difference on the surface.

  Subsequently, each image forming device 10 (Y, M, C, K) corresponds to the electrostatic latent image of each color component formed on the photosensitive drum 11 charged to a required polarity (minus polarity). Color (Y, M, C, K) toner is supplied from the developing roll 141 and electrostatically attached to perform development. By this development, the electrostatic latent images of the respective color components formed on the respective photosensitive drums 11 are visualized as toner images of four colors (Y, M, C, K) respectively developed with the corresponding color toners. It becomes.

  Subsequently, when each color toner image formed on the photosensitive drum 11 of each image forming device 10 (Y, M, C, K) is conveyed to the primary transfer position, the primary transfer device 15 (Y, M, C, K) are primarily transferred in such a manner that the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 21 that rotates in the direction indicated by the arrow B of the intermediate transfer device 20.

  Further, in each image forming device 10 (Y, M, C, K) for which the primary transfer has been completed, the drum cleaning device 16 removes the adhering matter so as to clean the surface of the photosensitive drum 11. Thereby, each image forming device 10 (Y, M, C, K) is brought into a state in which the next image forming operation is possible.

  Subsequently, in the intermediate transfer device 20, the toner image primarily transferred by the rotation of the intermediate transfer belt 21 is held and conveyed to the secondary transfer position. On the other hand, the paper feeding device 30 sends the required recording paper 5 to the paper feeding conveyance path 34 in accordance with the image forming operation. In the paper feed conveyance path 34, a pair of paper conveyance rolls 33 as registration rolls feeds the recording paper 5 to the secondary transfer position in accordance with the transfer timing.

  At the secondary transfer position, the secondary transfer device 26 performs secondary transfer of the toner image on the intermediate transfer belt 21 onto the recording paper 5 at once. Further, in the intermediate transfer device 20 after the secondary transfer is completed, the belt cleaning device 27 removes adhered matters such as toner remaining on the surface of the intermediate transfer belt 21 after the secondary transfer, and cleans it.

  Subsequently, the recording paper 5 onto which the toner image has been secondarily transferred is peeled from the intermediate transfer belt 21 and then conveyed to the fixing device 40 via the paper conveyance path 35. In the fixing device 40, the necessary fixing process (heating and heating) is performed by introducing and passing the recording sheet 5 after the secondary transfer through the contact portion between the rotating rotating body 41 for heating and the rotating body 42 for pressing. Pressure) to fix the unfixed toner image on the recording paper 5. Finally, the recording paper 5 after the fixing is completed is placed, for example, on the upper portion of the apparatus main body 1a by the paper discharge roll pair 38 in the image forming operation only for forming an image on one side thereof. The paper is discharged to the paper discharge unit 37.

  Through the above operation, the recording paper 5 on which a full color image formed by combining four color toner images is output.

[Monochrome mode]
Next, the operation in the monochrome mode for forming a monochrome toner image using only the black (K) imaging device 10K will be described.

  When the image forming apparatus 1 receives command information for a monochrome image forming operation (printing) request from a user interface (not shown), a printer driver, or the like, as shown in FIG. 3, prior to the image forming operation, The first surface exposing roll 24 is moved to the retracted position where it is retracted upward by the contact / separation means (not shown), and the color primary transfer roll 15 (Y corresponding to the color image forming device 10 (Y, M, C)). , M, C) move to the retracted position separated from the color photosensitive drums 11 (Y, M, C), and then the black (K) image forming device 10K, the intermediate transfer device 20, the secondary transfer device 26, The fixing device 40 and the like are started. In the image forming apparatus 1 according to this embodiment, monochrome (monochrome) is not performed by a user interface or printer driver (not shown) unless a full color image forming operation (print) is specified from a user interface or printer driver (not shown). ) Image forming operation (printing) is automatically selected.

  Further, the color primary transfer rolls 15 (Y, M, C) are separated from the intermediate transfer belt 21 in the retracted position, and are not in contact with the intermediate transfer belt 21. In the black and white mode, unlike the full color mode, the yellow (Y), magenta (M) and cyan (C) color image forming devices 10 (Y, M, C) and the color primary transfer roll 15 (Y, M, C) are not driven and are stopped.

  In the black (K) imaging device 10K, the photosensitive drum 11K rotates in the direction indicated by the arrow A, and the charging device 12K charges the surface of the photosensitive drum 11K to a required polarity (minus polarity) and potential, respectively. . Subsequently, the exposure device 13K irradiates the surface of the charged photosensitive drum 11K with light emitted based on a black and white image signal input to the image forming apparatus 1, and a required potential difference is applied to the surface. The electrostatic latent image of the component comprised by is formed.

  Subsequently, the developing device 14K supplies, from the developing roller 141, the corresponding black (K) toner charged to the required polarity (negative polarity) with respect to the black and white component electrostatic latent image formed on the photosensitive drum 11K. Each is supplied and electrostatically attached to develop. By this development, the electrostatic latent image formed on the photosensitive drum 11K is visualized as a toner image developed with the corresponding black toner.

  Subsequently, when the toner image formed on the photosensitive drum 11K of the image forming device 10K is conveyed to the primary transfer position, the primary transfer device 15K causes the toner image to move in the direction indicated by the arrow B of the intermediate transfer device 20. Primary transfer is performed on the rotating intermediate transfer belt 21.

  Further, in the image forming device 10K after the primary transfer is completed, the drum cleaning device 16K removes the adhering material so as to scrape off and cleans the surface of the photosensitive drum 11K. As a result, the image forming apparatus 10K is brought into a state in which the next image forming operation can be performed.

  Subsequently, in the intermediate transfer device 20, the toner image primarily transferred by the rotation of the intermediate transfer belt 21 is held and conveyed to the secondary transfer position. On the other hand, the paper feeding device 30 sends the required recording paper 5 to the paper feeding conveyance path 34 in accordance with the image forming operation. In the paper feed conveyance path 34, a pair of paper conveyance rolls 33 as registration rolls feeds the recording paper 5 to the secondary transfer position in accordance with the transfer timing.

  At the secondary transfer position, the secondary transfer device 26 performs secondary transfer of the toner image on the intermediate transfer belt 21 onto the recording paper 5 at once. Further, in the intermediate transfer device 20 after the secondary transfer is completed, the belt cleaning device 27 removes adhered matters such as toner remaining on the surface of the intermediate transfer belt 21 after the secondary transfer, and cleans it.

  Subsequently, the recording paper 5 onto which the toner image has been secondarily transferred is peeled from the intermediate transfer belt 21 and then conveyed to the fixing device 40 via the paper conveyance path 35. In the fixing device 40, the necessary fixing process (heating and heating) is performed by introducing and passing the recording sheet 5 after the secondary transfer through the contact portion between the rotating rotating body 41 for heating and the rotating body 42 for pressing. Pressure) to fix the unfixed toner image on the recording paper 5. Finally, the recording paper 5 after the fixing is completed is placed, for example, on the upper part of the image forming apparatus main body 1a by the paper discharge roll pair 38 in the image forming operation only for forming an image on one side thereof. The paper is discharged to the paper discharge unit 37.

  Through the above operation, the recording paper 5 on which a black and white image composed only of a black (K) toner image is formed is output.

<Configuration of Main Part of Image Forming Apparatus>
As shown in FIGS. 4 and 5, the intermediate transfer device 20 includes an intermediate transfer belt 21, a plurality of belt support rolls 22 to 25 disposed inside the intermediate transfer belt 21, and primary transfer as a primary transfer device. The rolls 15 (Y, M, C, K) and the like are integrally united to constitute an intermediate transfer unit 300 as an example of a detachable structure. The intermediate transfer unit 300 is detachable from the image forming apparatus main body 1a.

  The intermediate transfer unit 300 is arranged on the front side of the image forming apparatus main body 1a and has a substantially rectangular front frame 301 whose front shape is elongated, and the intermediate transfer unit 300 is arranged on the back side of the image forming apparatus main body 1a and has a substantially rectangular rear frame 302 which is elongated. And first and second connection frames 303 and 304 that connect the front frame 301 and the rear frame 302. A plurality of belt support rolls 22 to 26 that stretch the intermediate transfer belt 21 and a primary transfer roll 15 (Y, M, C, K) are rotatably supported on the front frame 301 and the rear frame 302. The rear frame 302 is provided with guide pins 305 and 306 for positioning when the intermediate transfer unit 300 is mounted on the image forming apparatus main body 1a so as to protrude toward the back side.

  Further, as shown in FIGS. 5 and 6, the primary transfer roll 15 (Y, M, C) and the first surface-developing roll 24 of the collar are moved to the retracted position inside the intermediate transfer unit 300. A retraction means 307 is arranged. The contact / separation means 307 includes a first arm member 308 (Y, M, C, K) having a substantially L-shaped front surface that rotatably supports the primary transfer roll 15 (Y, M, C, K), and a first arm. A second arm member 309 having a substantially L-shaped front surface that rotatably supports the surface-developing roll 24, a first arm member 308 (Y, M, C) excluding black, and a second arm member 309. A pair of slide members 310 and 311 to be rotated is provided. The first and second arm members 308 (Y, M, C, K), 309 are centered on the rotation fulcrums 312 (Y, M, C, K), 313 on the inner surfaces of the front frame 301 and the rear frame 302. Each is attached so as to be freely rotatable. In addition, the primary arm 308 (Y, M, C, K) is biased to the base end portion of the first arm member 308 (Y, M, C, K), and the primary transfer roll 15 ( A first coil spring 314 (Y, M, C, K) is provided as an urging means for bringing Y, M, C, K) into contact with the photosensitive drum 11. A second coil spring 315 serving as a biasing unit that biases the second arm member 309 and positions the first surface-exposing roll 24 at the operating position is provided at the base end portion of the second arm member 309. Is provided. The first and second coil springs 314 (Y, M, C, K), 315 are compression springs. In FIG. 6, reference numeral 231 denotes a third coil spring as a biasing unit that biases the tension applying roll 23 in the outward direction along the longitudinal direction of the intermediate transfer unit 300.

  As shown in FIGS. 5 and 6, the slide members 310 and 311 are provided with a long hole 318 in a rotatable drive shaft 316 and a fixed shaft 317 that are spanned between the front frame 301 and the rear frame 302. , 319, 320, and 321 are slidably disposed along the longitudinal direction of the intermediate transfer unit 300.

  Eccentric cams 322 and 323 for reciprocating the slide members 310 and 311 along the longitudinal direction of the intermediate transfer unit 300 are attached to the drive shaft 316. On the other hand, the slide members 310 and 311 are provided with cam followers 324 and 325 (see FIG. 5) with which the eccentric cams 322 and 323 abut. The slide members 310 and 311 are urged so that the cam followers 324 and 325 abut against the eccentric cams 322 and 323 by a coil spring or the like (not shown). The drive shaft 316 is rotationally driven at predetermined timings in the clockwise direction and the counterclockwise direction by the drive device 50 provided on the image forming apparatus main body 1a side via the coupling member 326.

  When switching from the full color mode to the black and white mode, as shown in FIG. 7, the eccentric cams 322 and 323 are rotationally driven by the driving device 50, and the slide members 310 and 311 are moved in the direction of arrow C via the cam followers 324 and 325. Move along. The first arm member 308 (Y, M, C) and the second arm member 309 are connected to the slide members 310 and 311, and are shown in the drawing as the slide members 310 and 311 move along the arrow C direction. It rotates counterclockwise. The primary transfer roll 15 (Y, M, C) of the collar rotatably provided on the first arm member 308 (Y, M, C) is connected to the photosensitive drum 11 (Y, M, C) and the middle. It moves to a retracted position separated from the transfer belt 21. Further, the first surface roll 24 that is rotatably provided on the second arm member 309 moves to the retracted position.

<Configuration of drive device>
On the back side of the image forming apparatus 1, as shown in FIG. 5, four image forming apparatuses 10 (Y, M, C, K), an intermediate transfer apparatus 20, a secondary transfer apparatus 26, a paper feeding apparatus 30, A driving device 50 for driving the fixing device 40 and the like is disposed.

  As shown in FIG. 8, the drive device 50 includes first to third drive motors 52 to 54 including a DC motor or the like as a drive source attached to the back surface of the housing 51 of the drive device 50. Yes. The first drive motor 52 which is a main motor mainly drives the four developing devices 14 (Y, M, C, K) of yellow, magenta, cyan, and black and the paper feeding device 30. The second drive motor 53, which is a drum motor, mainly drives the four photosensitive drums 11 (Y, M, C, K) of yellow, magenta, cyan, and black and the intermediate transfer belt 21. A third drive motor 54, which is a fuser motor, mainly drives the fixing device 40 and the paper discharge system.

  Further, as shown in FIG. 9, the drive device 50 includes a first drive device 55 that uses the first drive motor 52 as a drive source and a second drive device that uses the second drive motor 53 as a drive source. 56 and a third drive device 57 using the third drive motor 54 as a drive source.

  The second drive unit 56 includes a drive gear 59 (59K) that meshes with an output gear 58 provided on the output shaft of the second drive motor 53, and that rotates the black (K) photosensitive drum 11K. Yes. Further, the output gear 58 of the second drive motor 53 is engaged with a drive gear 121 for rotationally driving the drive roll 22 of the intermediate transfer unit 300 via the transmission gear 120. As shown in FIG. 5, the rotation shaft 122 of the drive gear 121 is connected to the drive roll 22 via a coupling member 327. In FIG. 5, reference numeral 123 denotes a drive gear that drives the fixing device 40 by the third drive motor 54.

  As shown in FIG. 10, the drive gear 59 is attached to a drive shaft 60 that rotationally drives the black (K) photosensitive drum 11K via a pin 61 (see FIG. 12). The drive shaft 60 is rotatably mounted with a transmission gear 62 that transmits a rotational driving force to the color photosensitive drums 11 (Y, M, C). Further, between the drive gear 59 and the transmission gear 62, a cup for a photoconductor as a drive force transmission mechanism that transmits or does not transmit (cuts off) the rotational drive force of the drive gear 59 to the transmission gear 62. A ring mechanism 63 is arranged.

  The transmission gear 62 is sandwiched between the first annular member 65a and the second annular member 65b, and movement of the drive shaft 60 along the axial direction is restricted. A coupling member 66 that is coupled to the photosensitive drum 11K and transmits a rotational driving force is mounted on the distal end side along the axial direction of the first annular member 65a. The coupling member 66 is pressed toward the photosensitive drum 11K by a coil spring 64. Further, the coupling member 66 is provided in a state in which the movement range is restricted by a pin 68 inserted into a first long hole 67 provided in the drive shaft 60 along the axial direction.

  As shown in FIG. 10, the photoconductor coupling mechanism 63 is roughly provided with a coupling member 71, a link member 72, and a cover member 73. As shown in FIG. 11, the coupling member 71 is formed in a substantially disc shape having a mounting hole 711 for mounting on the drive shaft 60 so as to be movable in the axial direction. Further, the end face of the coupling member 71 on the transmission gear 62 side is provided with first protrusions 712 provided at positions opposed to the outer peripheral part by 180 degrees so as to protrude in parallel with the axial direction. The first protrusion 712 is formed in a substantially trapezoidal shape, as viewed from the axial direction, surrounded by an outer peripheral surface and an inner peripheral surface formed in an arc shape and both end surfaces formed along the radial direction. Has been. In addition, a convex portion 713 that protrudes inward in the radial direction is provided on the inner peripheral surface of the first protrusion 712. The convex portion 713 is disposed at a position shifted in one direction (right direction in the drawing) from the central portion along the inner peripheral surface of each first projection portion 712. As a result, the two first protrusions 712 have an asymmetric shape with respect to the center line of the drive shaft 60. The drive gear 59 and the transmission gear 62 are phase-matched by the convex portion 713. In addition, the end surface of the coupling member 71 on the side of the drive gear 59 is provided with a second protrusion 714 that is formed relatively longer than the first protrusion 712 on the outer periphery thereof so as to protrude in parallel with the axial direction. I have. The second protrusion 714 is arranged so that the position along the circumferential direction is different from the first protrusion 712. For example, the second protrusion 714 is formed in the same shape as the shape of the first protrusion 712 and includes a protrusion 713.

  On the other hand, as shown in FIG. 12, the transmission gear 62 is formed in a shape similar to the first protrusion 712 of the coupling member 71, and the first recess 621 to which the first protrusion 712 is coupled is formed. Each is provided at a position facing 180 degrees. Further, as shown in FIG. 10, the drive gear 59 is formed in a shape similar to the second protrusion 714 of the coupling member 71, and at least one second recess to which the second protrusion 714 is coupled. 591. In this embodiment, in order to reduce the number of parts by sharing parts, the drive gear 59 and the transmission gear 62 use the same gear, and the drive gear 59 has a second recess 591. Two are provided.

  Moreover, since the 1st projection part 712 is provided with the convex part 713 arrange | positioned in the asymmetrical position with respect to the centerline of the drive shaft 60, the coupling member 71 and the transmission gearwheel 62 followed the circumferential direction. The coupling member 71 and the transmission gear 62 are in phase with each other (position along the circumferential direction). Further, the second projecting portion 714 also includes a convex portion 713 similarly to the first projecting portion 712. Therefore, the coupling member 71 and the drive gear 59 are configured to be coupled to each other only at one place along the circumferential direction, and the phase between the coupling member 71 and the drive gear 59 (position along the circumferential direction). Are combined. As a result, when the drive gear 59 is connected to the transmission gear 62 via the coupling member 71, the phases of the drive gear 59 and the transmission gear 62 always coincide.

  In addition, a coil spring 74 that presses the coupling member 71 in a direction away from the drive gear 59 is disposed between the drive gear 59 and the coupling member 71 as shown in FIG. The movement range of the coupling member 71 is restricted by a pin 76 inserted in a second long hole 75 provided in the drive shaft 60 along the axial direction.

  As shown in FIG. 11C, the link member 72 is formed in an annular shape, and includes a lever 721 provided on the outer periphery of the annular portion so as to protrude outward in the radial direction. ing. Further, on the outer peripheral surface of the link member 72, convex portions 723 each having an inclined surface 722 are provided at positions facing each other by 180 degrees.

  The cover member 73 is formed in a cylindrical shape that covers the outer periphery of the link member 72, as shown in FIG. An inner surface of the cover member 73 is provided with an inclined surface 731 that comes into contact with the convex portion 723 of the link member 72. Further, the cover member 73 is provided with an opening 732 for projecting the lever 721 of the link member 72 outward over a required angle. The cover member 73 is attached in a state of being fixed to a housing (not shown) of the driving device 50.

  Therefore, by rotating the link member 72 via the lever 721, the link member 72 comes into contact with the inclined surface 731 of the cover member 73 on which the inclined surface 722 of the convex portion 723 is fixed and is pushed along the axial direction. As the link member 72 moves, the link member 72 pushes the coupling member 71 toward the transmission gear 62 along the axial direction. As shown in FIG. The two projections 714 and the second recess 591 of the drive gear 59 are disconnected, and the transmission of the rotational driving force from the drive gear 59 to the transmission gear 62 is interrupted. Further, the link member 72 rotates the lever 721 in the reverse direction, so that the coupling member 71 is pushed toward the drive gear 59 along the axial direction by the link member 72, and the second protrusion of the coupling member 71. The portion 714 is coupled to the second recess 591 of the drive gear 59, and the rotational driving force is transmitted from the drive gear 59 to the transmission gear 62.

  As shown in FIG. 12, the transmission gear 62 attached to the drive shaft 60 of the black photosensitive drum 11 </ b> K receives cyan, magenta, and yellow photosensitive drums 11 (C, M, Y) via an intermediate gear 77. ) And the drive gear 59 (59C, 59M, 59Y). The drive gear 59 (59K, 59C, 59M, 59Y), the transmission gear 62, and the intermediate gear 77 constitute a drive force transmission unit of the second drive device 56.

  On the other hand, as shown in FIG. 9, the first driving device 55 receives a rotational driving force from an output gear 78 provided on the driving shaft of the first driving motor 52, and develops a black (K) developing device 14K. Are provided with a transmission gear 79 and a driving gear 80 for transmitting a driving force to the motor. The black (K) developing device 14K is driven to rotate by the drive gear 80.

  Coupled to the transmission gear 79 is a developing device coupling mechanism 82 as a driving force transmission mechanism for transmitting a rotational driving force to the color developing device 14 (Y, M, C) via a driven gear 81. . The developing device coupling mechanism 82 basically has the same configuration as the photoconductor coupling mechanism 63.

  As shown in FIG. 13, the developing device coupling mechanism 82 is roughly provided with a coupling member 83, a link member 84, and a cover member 85 (see FIG. 12). The coupling member 83 is formed in a substantially disc shape having a mounting hole 831 for mounting on a rotating shaft (not shown). In the coupling mechanism 82 for the developing device, a driving gear 86 and a transmission gear 87 are arranged on the same side along the axial direction of the coupling member 83, unlike the coupling mechanism 63 for the photoconductor. . The drive gear 86 is meshed with the driven gear 81.

  On the end face of the coupling member 83 on the side of the drive gear 86 and the transmission gear 87, there are provided two protrusions 832 provided on the outer periphery of the coupling member 83 at positions opposed to each other by 180 degrees so as to protrude in parallel with the axial direction. The protruding portion 832 is formed in a substantially trapezoidal shape surrounded by an outer peripheral surface and an inner peripheral surface formed in an arc shape when viewed from the axial direction, and both end surfaces formed along the radial direction. . However, unlike the photoconductor coupling mechanism 63, the protrusion 832 is not provided with a protrusion corresponding to the protrusion 713.

  On the other hand, the drive gear 86 and the transmission gear 87 are formed in a similar shape to the protrusion 832 of the coupling member 83, and are provided with recesses 861, 871 to which the protrusion 832 is coupled at positions facing each other by 180 degrees. In this embodiment, the drive gear 86 and the transmission gear 87 use the same gear in order to reduce the number of components by sharing the components.

  Further, a coil spring 88 is disposed between the inner surface of the cover member 85 and the coupling member 83, and the coupling member 83 is coupled to the drive gear 86 and the transmission gear 87 (downward in the figure). ).

  The link member 84 is formed in an annular shape, similar to that shown in FIG. 11C, and a lever 841 provided on the outer periphery of the annular portion so as to protrude toward the outer periphery in the radial direction. It has. Further, on the outer peripheral surface of the link member 84, a convex portion 843 having an inclined surface 842 is provided at a position facing each other by 180 degrees.

  As illustrated in FIG. 12, the cover member 85 is formed in a covered cylindrical shape that covers the outer periphery of the link member 84. The inner peripheral surface of the cover member 85 is provided with an inclined surface (not shown) that comes into contact with the convex portion 843 of the link member 84 as in the case shown in FIG. Further, the cover member 85 is provided with an opening (not shown) through which a lever 841 of the link member 84 is passed over a required angle. The cover member 85 is attached in a fixed state with respect to a housing (not shown) of the drive device 50.

  Therefore, the link member 84 is pushed and moved along the axial direction by rotating the lever 841 so that the inclined surface 842 of the convex portion 843 contacts an inclined surface (not shown) of the cover member 85. As the link member 84 moves, the coupling member 83 is pushed by the link member 84 along the axial direction toward the drive gear 86 and the transmission gear 87, and the projection 832 of the coupling member 83, the drive gear 86, The recesses 861 and 871 of the transmission gear 87 are coupled, and the rotational driving force is transmitted from the drive gear 86 to the transmission gear 87.

  Further, the link member 84 is pushed and moved along the axial direction by rotating the lever 841 in the reverse direction so that the inclined surface 842 of the convex portion 843 contacts an inclined surface (not shown) of the cover member 85. As the link member 84 moves, the coupling member 83 moves in the axial direction away from the drive gear 86 and the transmission gear 87, and the projection 832 of the coupling member 83 and the recess 871 of the transmission gear 87 And the transmission of the rotational driving force from the drive gear 86 to the transmission gear 87 is interrupted.

  As shown in FIG. 13, drive gears 80 are meshed with input gears (not shown) of the color developing device 14. Further, the driving force 80 is sequentially transmitted to the adjacent drive gear 80 of the color developing device 14 via the intermediate gear 81. The drive gear 80, the drive gear 86, the transmission gear 87, the input gear and the intermediate gear 81 constitute a drive force transmission unit of the second drive device 66.

  FIG. 14 is a block diagram showing a drive switching device according to this embodiment.

  The drive switching device 92 uses the drive motor 54 of the third drive device 57 as a drive source. This drive motor 54 is rotationally driven only in one direction. The drive switching device 92 is broadly divided into a driving gear 93 to which a rotational driving force is transmitted from the third driving motor 54 and a small diameter portion of the driving gear 93 that is intermittently engaged with the driving gear 2 2. The stepped tooth missing gear 94, the solenoid 95 and the torsion spring 96 for intermittently driving the tooth missing gear 94, and the tooth missing gear 94 are selectively meshed with each other to change the transmission direction of the driving force. A first switching gear 97 that switches to the first direction, and second switching gears 98 and 99 that are selectively meshed with the tooth-missing gear 94 and switch the transmission direction of the driving force to the second direction. Yes.

  As shown in FIG. 15, the tooth-missing gear 94 is integrated with a large-diameter portion 941 formed in a hollow cylindrical shape having a relatively large outer diameter and one end side along the axial direction of the large-diameter portion 941. A small-diameter portion 942 formed in a hollow cylindrical shape having an outer diameter relatively smaller than that of the large-diameter portion 941, and disposed along the axial direction over the centers of the large-diameter portion 941 and the small-diameter portion 942. And a shaft support portion 943 formed in an elongated cylindrical shape that is rotatably supported by a rotation shaft of a housing (not shown).

  The tooth missing gear 94 includes a first tooth missing portion 944 and a second tooth missing portion 945 provided on the outer periphery of the large diameter portion 941 so as to have different positions in the axial direction and the radial direction. The 1st tooth missing part 944 and the 2nd tooth missing part 945 are formed in the shape symmetrical with respect to the centerline of a rotating shaft. The first tooth missing portion 944 and the second tooth missing portion 945 are formed so as to form a central angle smaller than 180 ° along the circumferential direction of the large diameter portion 941. Further, between the first tooth missing portion 944 and the second tooth missing portion 945, gap portions 946, 947 in which teeth are not formed on the outer periphery of the large diameter portion 941 are provided at positions facing each other by 180 °. It has been.

  Further, the first and second tooth missing portions 944 and 945 have different positions along the axial direction on the upstream side and the downstream side along the circumferential direction, and are formed in two stages integrally formed in the intermediate portion. It is formed as a gear. More specifically, in the first and second tooth missing portions 944 and 945, upstream regions (upstream portions) 944a and 945a along the circumferential direction are arranged near one end portion along the axial direction, and the circumferential direction thereof. Downstream regions (downstream portions) 944b and 945b along the axis are disposed closer to the other end along the axial direction. The upstream regions (upstream portions) 944a and 945a and the downstream regions (downstream portions) 944b and 945b are formed so as to overlap each other at the intermediate portions 944c and 945c.

  Further, the first and second tooth missing portions 944 and 945 are provided with notch portions 948 that are notched over a required length on the inner peripheral side of the upstream end portions 944a ′ and 945a ′ along the circumferential direction. The upstream end portions 944a ′ and 945a ′ are elastically deformable toward the inner peripheral side. The number of teeth of the upstream ends 944a 'and 945a' is set to about 3 to 5 teeth, for example.

  As shown in FIGS. 14 and 15, the small-diameter portion 942 of the tooth-missing gear 94 has a locking portion 949 for stopping the rotation by hooking the hook 951 of the solenoid 95 on the outer peripheral surface at a position different by 180 °. Each is provided. The small-diameter portion 942 of the tooth-missing gear 94 includes an activation portion 940 that is formed in a flat plate shape along the diametrical direction in a state of protruding from the end portion along the axial direction. One linear portion 962 of the torsion spring 96 is in pressure contact with the starting portion 940, and an elastic force in the counterclockwise direction in the drawing is applied to the tooth missing gear 94. The torsion spring 96 includes a circular portion 961 in which a linear member having elasticity is wound in a circular shape, and first and second linear portions 962 formed linearly in a tangential direction with respect to the circular portion 961. 963. The circular portion 961 of the torsion spring 96 is disposed in a state of being positioned in a housing (not shown). Further, the position of the second linear portion 963 is restricted by a housing (not shown), and a downward pressing force is applied to the first linear portion 962.

  Further, the tooth-missing gear 94 has first and second switching gears 97 that are rotationally driven by a required amount by being intermittently meshed with the tooth-missing gear 94 at a position opposite to the driving side thereof. 98,99 are arranged. As the first and second switching gears 97, 98, 99, for example, the same gear is used. The second switching gear 98 is engaged with a second switching gear (reversing gear) 99 that reverses the rotation direction.

  Further, on one side of the first and second switching gears 97 and 98, an operation plate 100 that is operated to switch the connection state of the coupling mechanism 63 on the photosensitive member side and the coupling mechanism 82 on the developing device side is disposed. ing. As shown in FIG. 16, the operation plate 100 is formed in an elongated prismatic shape, and is attached to the housing 51 of the driving device 50 so as to be movable in the vertical direction via the two rotating rollers 101 and 102. ing. In addition, the operation plate 100 includes first and second rack gears 103 and 104 that mesh with the first switching gear 97 and the reverse gear 99, respectively, on one side surface of the upper end portion thereof. Further, the operating plate 100 includes a third rack gear 105 on one side surface of the intermediate portion thereof. The third rack gear 105 is engaged with a drive gear 110 that rotationally drives eccentric cams 322 and 323 (see FIG. 6).

  The first and second rack gears 103 and 104 of the working plate 100 are formed to have a predetermined number of teeth at predetermined positions. Similarly, the third rack gear 105 is formed to have a predetermined number of teeth at a predetermined position.

  Further, a first recess 106 that engages with the link member 72 of the coupling mechanism 63 on the photosensitive member side is provided on the other side surface of the intermediate portion of the operation plate 100. Furthermore, a second recess 107 that engages with the link member 84 of the coupling mechanism 82 on the developing device side is provided on one side surface of the lower end portion of the operation plate 100.

  Further, as shown in FIG. 9, a projection (not shown) for detecting the home position of the operation plate 100 by the home position sensor 108 attached to the housing 51 side is provided on the front surface of the lower end portion of the operation plate 100. It has been.

  By the way, the image forming apparatus 1 according to the present embodiment considers that the image forming apparatus 1 is mainly used in the black and white mode, and executes the image forming operation in the full color mode and then at the end of the image forming operation in the full color mode. It is configured to automatically switch to the mode and stop the device. As shown in FIG. 7, when the image forming apparatus 1 is switched from the full color mode to the monochrome mode, the first surface roll 24 moves to the retracted position and the color primary transfer rollers 15 (Y, M, C) is separated from the photosensitive drum 11 and the intermediate transfer belt 21. As a result, the intermediate transfer belt 21 has a tension length L along the circumferential direction stretched between the black primary transfer roller 15K and the tension applying roll 23, and the first surface-developing roll 24 is moved to the retracted position. Compared to the full color mode, the amount of movement is shorter. Therefore, in order to maintain the tension of the intermediate transfer belt 21, the tension applying roll 23 moves by a distance Δα toward the outside along the longitudinal direction of the intermediate transfer unit 300, as shown in FIG. When the tension applying roll 23 moves outward along the longitudinal direction of the intermediate transfer unit 300, the tension applying roll 23 slightly rotates along the counterclockwise direction in the drawing. Further, the intermediate transfer belt 21 stretched around the tension applying roll 23 moves in the reverse direction as the tension applying roll 23 rotates.

  As shown in FIG. 24, a cleaning plate 271 of a belt cleaning device 27 is brought into contact with the tension applying roll 23 in a direction opposite to the moving direction of the intermediate transfer belt 21 via the intermediate transfer belt 21. Yes. Therefore, as shown in FIG. 24B, the edge portion 271a of the cleaning plate 271 of the belt cleaning device 27 is released from the contact state with the surface of the intermediate transfer belt 21 when the intermediate transfer belt 21 moves in the reverse direction. Deforms in the direction to be done.

  Since the image forming apparatus 1 shifts to the black and white mode at the end of the full color mode, when the next image forming operation starts, the tension applying roll 23 rotates in the clockwise direction, which is the normal rotation direction, and the intermediate transfer belt 21 also rotates in the normal direction. Move in the rolling direction. Then, the edge portion 271a of the cleaning plate 271 of the belt cleaning device 27 is bent along the moving direction of the intermediate transfer belt 21, as shown in FIG.

  As described above, in the image forming apparatus 1, when the image forming operation is performed in the full color mode, the cleaning plate 271 of the belt cleaning device 27 is in contact with the surface of the intermediate transfer belt 21 and the surface of the intermediate transfer belt 21 is contacted. The state in which the contact is released is repeated. For this reason, the cleaning plate 271 of the belt cleaning device 27 may be damaged due to repeated fatigue at the edge portion in contact with the surface of the intermediate transfer belt 21 and may cause poor cleaning.

  Therefore, in this embodiment, the control device 200 controls the driving device 50 to move the intermediate transfer belt 21 in the reverse direction along with the movement of the tension applying roll 23 when switching from the full color mode to the monochrome mode. The intermediate transfer belt 21 is driven to rotate in the forward direction at the above speed.

<Operation of Characteristic Part of Image Forming Apparatus>
In the image forming apparatus 1 of this embodiment, prior to the start of the image forming operation, the control apparatus 200 has selected either the full color mode or the monochrome mode by the user via a user interface or a print driver (not shown). Determine.

  When it is determined that the user has selected the full color mode, the control device 200 activates the third drive motor 54 for a predetermined time and turns on the solenoid 95 as shown in FIG. Then, as shown in FIG. 18, the hook 951 of the solenoid 95 is disengaged from the engaging portion 949 of the chipped gear 94, and the starter 940 of the chipped gear 94 has a first linear portion 962 of the torsion spring 96. And is rotated counterclockwise in the figure. The solenoid 95 is turned off after the hook 951 is released and before the tooth missing gear 94 is rotated 180 °.

  When the toothless gear 94 is rotationally driven in the counterclockwise direction in the drawing, the tip end portion 944a ′ of the first toothless portion 944 is rotated with the small diameter portion of the drive gear 93 that is rotationally driven by the third drive motor 54. Engage. Thereafter, the chipped gear 94 is rotationally driven in the counterclockwise direction in the drawing by the drive gear 93 as shown in FIG. At this time, the first tooth missing portion 944 of the tooth missing gear 94 stably meshes with the drive gear 93, so that the tooth missing gear 94 is shown in the drawing at a constant speed by the rotational driving force transmitted from the drive gear 93. Rotates counterclockwise.

  After the first tooth missing portion 944 of the tooth missing gear 94 is stably meshed with the drive gear 93 (about three teeth), as shown in FIG. 19, the second tooth missing portion 945 becomes the second switching gear. The second switching gear 98 is rotated in the clockwise direction in the drawing. Further, the rotational driving force of the second switching gear 98 is reversed in the rotation direction by the reversing gear 99, and then the operation plate 100 is moved upward by the second rack gear 104 that meshes with the reversing gear 99.

  As the operating plate 100 moves upward, the link member 72 of the photoconductor side coupling mechanism 63 inserted into the first and second recesses 106 and 107 of the operating plate 100 and the coupling mechanism 82 on the developing device side. The link member 84 rotates. As shown in FIG. 10, the coupling mechanism 63 on the photosensitive member side causes the coupling member 71 to be pushed toward the drive gear 59 as the lever 721 of the link member 72 is rotated upward. The second protrusion 714 is coupled to the second recess 591 of the drive gear 59. As a result, the rotational driving force of the drive gear 59 is transmitted to the transmission gear 62 when the drive gear 59 is driven. At the time of image formation, the transmission gear 62 is driven to rotate, so that the drive gear 59 provided on the drive shaft of the color photosensitive drum 11 (Y, M, C) via the intermediate gear 77 that meshes with the transmission gear 62. The color photosensitive drums 11 (Y, M, C) are driven to rotate.

  On the other hand, in the coupling mechanism 82 on the developing device side, when the lever 841 of the link member 84 rotates upward, the coupling member 83 is pushed toward the drive gear 86 and the driven gear 87 as shown in FIG. Then, the protrusion 832 of the coupling member 83 is coupled to the recesses 861 and 871 of the drive gear 86 and the driven gear 87. As a result, the rotational driving force of the drive gear 86 is transmitted to the transmission gear 87, and the transmission gear 87 is rotationally driven. As shown in FIG. The developing device 14 (Y, M, C) is rotationally driven.

  Further, when the operation plate 100 moves upward, the drive gear 110 meshed with the third rack gear 105 of the operation plate 100 is rotationally driven, and the eccentric cams 322 and 323 are rotationally driven in the clockwise direction in FIG. As a result, the primary transfer roll 15 (Y, M, C) of the color image forming device 10 (Y, M, C) is moved downward, and the first surface roll 24 is moved to the operating position, The primary transfer roll 15 (Y, M, C) and the intermediate transfer belt 21 are brought into contact with the photosensitive drum 11 (Y, M, C).

  The timing at which the operating plate 100 drives the lever of the link member and the timing at which the eccentric cam 204 is driven by the third rack gear 105 of the operating plate 100 are set so as to be shifted from each other as shown in FIG. Thus, the load on the drive motor 84 is reduced.

  As shown in FIG. 20, when the operation plate 100 moves upward by a certain amount, the second rack gear 104 comes off from the reverse gear 99 and stops. Further, the tooth missing gear 94 is disengaged from the second switching gear 98 after the meshing between the upstream portion 945a of the second tooth missing portion 945 and the second switching gear 98 is completed. Thereafter, in the tooth missing gear 94, the first tooth missing portion 944 is disengaged from the drive gear 83. Further, as shown in FIG. 21, the tooth-missing gear 94 rotates in the counterclockwise direction in FIG. 21 when the starting portion 940 is pressed by the elastic force of the first linear portion 962 of the torsion spring 96. The hook 951 of the solenoid 95 is locked to the portion 949 and stops. At this time, the first switching gear 97 is in mesh with the first rack gear 103 of the operating plate 100 as shown in FIG.

  Thereafter, the control device 200 drives the photosensitive drum 11 and the developing device 14 by rotating the first and second drive motors 52 and 53, and starts a full-color image forming operation.

  On the other hand, when it is determined that the image forming operation in the full color mode has been completed, the control device 200 activates the third drive motor 54 and turns on the solenoid 95 as shown in FIG. Then, the hook 951 of the solenoid 95 is disengaged from the locking portion 949 of the tooth missing gear 94, and the tooth missing gear 94 is pressed by the elastic force of the first linear portion 962 of the torsion spring 96 of the tooth missing gear 94. It is rotationally driven (activated) in the counterclockwise direction.

  When the tooth missing gear 94 is driven to rotate in the counterclockwise direction in the drawing, the tip end portion 945 a ′ of the second tooth missing portion 945 is meshed with the drive gear 93 that is rotationally driven by the drive motor 54.

  After the second tooth missing portion 945 of the tooth missing gear 94 is stably meshed with the drive gear 93 (about three teeth), as shown in FIG. 22, the first tooth missing portion 944 is the first switching gear. The first switching gear 97 is rotationally driven in the clockwise direction in the figure. The rotational driving force of the first switching gear 97 is transmitted to the first rack gear 103 of the operation plate 100, and the operation plate 100 moves downward.

  As the operation plate 100 moves downward, the link member 72 of the photoconductor side coupling mechanism 63 inserted into the first and second recesses 106 and 107 of the operation plate 100 and the coupling mechanism 82 on the developing device side. The link member 84 rotates. As shown in FIG. 10, the coupling mechanism 63 on the photosensitive member side causes the coupling member 71 to be pushed toward the transmission gear 62 as the lever 721 of the link member 72 is rotated downward. The second protrusion 714 is disengaged from the second recess 591 of the drive gear 59. As a result, when the drive gear 59 is driven, the rotational driving force of the drive gear 59 is not transmitted to the transmission gear 62, and only the black photosensitive drum 11 is rotationally driven.

  On the other hand, in the coupling mechanism 82 on the developing device side, as the lever 841 of the link member 84 rotates downward, the coupling member 83 is separated from the drive gear 86 and the transmission gear 87 as shown in FIG. The protrusion 832 of the coupling member 83 is disengaged from the recess 871 of the transmission gear 87. As a result, the rotational driving force of the drive gear 86 is not transmitted to the transmission gear 87, the color developing device 14 is stopped, and only the black developing device 14 is rotationally driven.

  Further, when the operation plate 100 moves downward, the drive gear 110 meshed with the third rack gear 105 of the operation plate 100 is rotationally driven, and the eccentric cams 322 and 323 are rotated counterclockwise in FIG. By driving, the first surface-developing roll 24 and the primary transfer roll 15 (Y, M, C) of the color are moved to the upper retracted position, and the primary transfer roll 15 (Y, M, C) and the intermediate transfer belt are moved. 21 is separated from the photosensitive drum 11.

  As shown in FIG. 14, when the operation plate 100 moves upward by a certain amount, the first rack gear 103 is disengaged from the first switching gear 97 and the second rack gear 104 is moved to the second switching gear 99. Stops while meshing with

  At this time, when the first surface-exposing roll 24 and the primary transfer rolls 15 (Y, M, C) of the collar move to the upper retracted position, the tension applying roll 23 is tensioned by the intermediate transfer belt 21 as described above. 23, as shown in FIG. 23, the intermediate transfer unit 300 moves outward by a distance Δα along the longitudinal direction. When the tension applying roll 23 moves outward along the longitudinal direction of the intermediate transfer unit 300, the tension applying roll 23 slightly rotates along the counterclockwise direction in the drawing. Further, the intermediate transfer belt 21 stretched around the tension applying roll 23 moves in the reverse direction as the tension applying roll 23 rotates.

  In this embodiment, the driving device 50 is controlled by the control device 200, and at the time of switching from the full color mode to the black and white mode, the moving speed V1 or higher at which the intermediate transfer belt 21 moves in the reverse rotation direction with the movement of the tension applying roll 23. The intermediate transfer belt 21 is rotationally driven in the forward rotation direction at a speed V2.

  More specifically, as shown in FIG. 17, when switching from the full color mode to the black and white mode, the control device 200 rotates the third drive motor 54, which is a fuser motor, to move the operation plate 100 downward. Thus, the drive gear 110 meshed with the third rack gear 105 of the working plate 100 is rotationally driven. Then, the drive shaft 316 connected to the drive gear 110 via the coupling portion 326 is rotationally driven, and the first and second shafts 321 and 323 are attached to the first and second by the eccentric cams 322 and 323 attached to the drive shaft 316. The arm members 308 and 309 are rotated. Then, as the first surface-expanding roll 24 rotatably attached to the second arm member 309 moves to the retracted position, the tension applying roll 23 rotates counterclockwise, and the intermediate transfer belt 21. Rotates in the reverse direction.

  Therefore, in this embodiment, the control device 200 rotates the second drive motor 53 in synchronization with the rotational drive of the third drive motor 54, and moves the intermediate transfer belt 21 in the forward rotation direction at the speed V2. Rotate. Specifically, in the image forming apparatus 1 of this embodiment, when the full color mode is switched to the black and white mode, the movement amount of the tension applying roll 23 is Δα (= about 0.7 mm), and the intermediate transfer belt 21 is reversed. The moving speed V1 in the direction is about 0.69 mm / s. Therefore, the image forming apparatus 1 drives the intermediate transfer belt 21 to rotate in the forward direction at a moving speed V2 faster than the speed V1 while switching from the full color mode to the black and white mode.

  Therefore, according to the above embodiment, it is possible to avoid the intermediate transfer belt 21 from rotating in the reverse direction when switching from the full color mode to the black and white mode, and as shown in FIG. The cleaning plate 271 of the cleaning device 27 can always be brought into contact with the intermediate transfer belt 21 while being bent in the forward rotation direction. Therefore, it is possible to suppress the cleaning plate 271 of the belt cleaning device 27 from being damaged as compared with the case where the roll that the contact member contacts via the belt rotates in the reverse direction when the image forming mode is switched.

  Thereafter, the control device 200 drives the black photosensitive drum 11K and the developing device 14K by rotationally driving the first and second drive motors 52 and 53, and starts a monochrome image forming operation.

  In the above-described embodiment, the case where the contact member is the cleaning plate 271 of the belt cleaning device 27 has been described. However, any contact member that is damaged when the roll rotates in the reverse direction when the image forming mode is switched can be used. Other members may be used.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 1a ... Image forming apparatus main body 21 ... Intermediate transfer belt 22 ... Drive roll 23 ... Tension applying roll 24 ... First surface-exposing roll 27 ... Belt cleaning apparatus 271 ... Cleaning plate (contact member)
300: Intermediate transfer unit

Claims (4)

An endless belt stretched between a plurality of rolls;
Drive means for rotationally driving the belt;
A contact member that contacts a surface of a belt stretched around one of the plurality of rolls;
Switching means for switching an image forming mode by displacing at least one of the plurality of rolls;
With
An image forming apparatus in which, when switching is performed by the switching unit, the belt is rotated in the forward direction by the driving unit at a speed equal to or higher than a rotational speed at which the roll with which the contact member contacts via the belt rotates in the reverse direction.   The image forming apparatus according to claim 1, wherein the belt is stretched on a plurality of rolls including a tension applying roll, and the contact member is in contact with the belt stretched on the tension applying roll. The image forming apparatus has a full color mode and a monochrome mode as image forming modes,
The image forming apparatus according to claim 1, wherein the switching unit switches the image forming mode to the monochrome mode at the end of the image forming operation in the full color mode.   4. The roll disposed adjacent to the downstream side of the tension applying roll in the belt moving direction moves to the retracted position when the image forming mode is switched from the full color mode to the monochrome mode. The image forming apparatus described in 1.

Images